Organic synthesis by condensation reactions resulting in the loss of a molecule of water or of ammonia are well known in the art. Certain of such reactions are generally effected in the presence of acidic catalysts. An important area in which such acid catalysis has been employed is in cyclization reactions as in the synthesis of triethylenediamine and its C-substituted homologues. The catalysts more generally used or proposed for use in such cyclization reactions are solid products of the Lewis acid type.
Triethylenediamine, also called diazabicyclo -[2.2.2]- octane, has been widely employed commercially as a catalyst in organic isocyanate reactions with compounds containing labile hydrogen, as in the production of urethane polymers. Triethylenediamine (sometimes hereinafter referred to as TEDA) was initially prepared in significant quantities by methods such as that described in U.S. Pat. No. 2,937,176, by passing aliphatic amines in vapor phase over acidic cracking catalyst, such as silica-alumina dried gel or acid activated clays. Numerous other feed stocks as well as other catalysts are disclosed in subsequent patents for preparation of TEDA as well as C-alkyl derivatives thereof.
Typical among these are U.S. Pat. Nos. 2,985,658 and 3,166,558 employing preferably silica-alumina type catalyst, but listing also other useful solid acid catalysts that can be employed such as alumina in which phosphate or fluoride ion is incorporated (U.S. Pat. No. 2,985,658). It is disclosed in U.S. Pat. No. 3,166,558 that while these reactions can take place under superatmospheric pressures, they offer no advantage over atmospheric or subatmospheric pressure.
Among other catalysts proposed in the patent art for preparation of triethylene diamine and/or C-alkyl homologues thereof, are certain phosphate compounds, particularly aluminum phosphate.
The use of aluminum phosphate as a catalyst in the preparation of heterocyclic compounds from aliphatic amines was early disclosed in U.S. Pat. No. 2,467,205, particularly for the preparation of piperazine from ethylenediamine or from polyethylene polyamine. The use of aluminum phosphate as catalyst in the preparation of triethylenediamine accompanied by piperazine among other by-products in further described in U.S. Pat. No. 3,172,891; while U.S. Pat. No. 3,342,820 describes the use of complex phosphates of alkali metal and trivalent metals in the preparation of C-alkyl TEDA.
U.S.S.R. Inventor's Certificate No. 525,681 discloses that the known processes for the preparation of TEDA by the catalytic conversion of various amines use aluminosilicate cracking catalysts, alumina with different additives, tungsten oxide or phosphates of metals at temperatures of 220.degree. to 550.degree. C., under pressures of 0.1 to 150 atm. (absolute), in the presence of various diluents.
U.S. Pat. No. 3,297,701 discloses as catalysts for preparation of TEDA and C-alkyl TEDA, in addition to the preferred aluminum phosphate stated to be superior, other phosphate compounds including calcium and iron phosphates among other listed metal phosphates. In the conversion of N-aminoethylpiperazine to triethylenediamine over aluminum phosphate catalyst, at most up to 39 mol % triethylenediamine is said to be obtained. Other of the named metal phosphate catalysts in the examples of the patent obtain yields of less than 10 mol % TEDA.
Acid metal phosphate catalysts, particularly phosphates of boron, aluminum and trivalent iron, have also been proposed for use in intramolecular cyclic dehydration reactions and other condensation reactions involving amino compounds. Examples of such reactions are found in U.S. Pat. No. 4,117,227, which discloses conversion of an N-substituted diethanolamine to the corresponding N-substituted morpholine. These condensation reactions are carried out in liquid phase at a temperature of from about 190.degree. C. to about 260.degree. C. and at any pressure to maintain reactants in a liquid state, i.e. generally from about 10 to about 1000 psig. U.S. Pat. No. 4,036,881 describes preparation of non-cyclic polyalkylene polyamines by condensation of an alkylene diamine with an ethanolamine. N-hydroxethylmorpholine is condensed with morpholine in the presence of aluminum phosphate catalyst at temperatures from about 240.degree. to 300.degree. C. and pressures of about 200 to 500 psig to form dimorpholino ethane according to U.S. Pat. No. 4,103,087. Similarly, dimorpholinodiethyl ether is obtained by condensation of hydroxyethyl morpholine with aminoethyl morpholine over iron, aluminum or boron phosphate in U.S. Pat. No. 4,095,022. Reaction of piperazine with ethanolamine over such acidic metal phosphate at a temperature of from about 250.degree. to about 350.degree. C. and a pressure ranging from about 200 psig to about 500 psig produces N-aminoethyl piperazine according to U.S. Pat. No. 4,049,657. U.K. Pat No. 1,492,359 discloses the preparation of morpholine compounds by reacting an aminoalkoxyalkanol compound over phosphoric acid and similar types of phosphorus-containing substances.
Pyrophosphates of lithium, sodium, strontium and barium have been used as dehydration catalysts; see U.S. Pat. 3,957,900. Phosphates and pyrophosphates of strontium and nickel have been used for the dehydrogenation of, for example, n-butene to butadiene under the conditions described in U.S. Pat. No. 3,541,172.